Satoshi Hirano
除了对发动机的温度进行控制以外，另一
种措施是防止累积在发动机油中的降质燃
料发生聚合反应。这需要防止氧化。Hirano
说，润滑油制造商需要在这方面努力。
Hirano承认在现实生活中，汽油发动机
中存在降质的燃料是不可避免的。但是，减
少不溶物的生成是可能的。“发动机油为了
实现更好的抗氧化性能，有两种方法：更好
的抗氧化剂配方，更高质量的基础油。这对
防止发动机结焦非常重要，”他说。
level of aromatics. In Japan, the aro-
matics can be as high as 40%. The ar-
omatic content could have an impact
on combustion by-product formation,
Hirano noted during the panel discus-
sion which followed his presentation
during the SAE F&L Asian Steering
Committee Colloquia.
“They are prone to formmore
insolubles than other hydrocarbons.
Actually by taking premium fuel in the
Japanese market, we are increasing
stress on coking. So from that view-
point, fuel quality is very important
when we take this technical assess-
ment of this phenomena,” Hirano said.
Toyota researchers also looked at
what could be done to prevent the
problem. They examined, for instance,
two different methods for cooling the
turbocharger, taking temperature
measurements at different locations.
These showed that dropping the
bearing temperature from about 215
o
C of an air-cooled turbocharger con-
dition to less than 160
o
C of the same
engine equipped with a cooling circuit
significantly reduced coking. Indeed,
at around 140
o
C, deposits were nearly
eliminated. In contrast, the uncooled
engine bearings from the hot engine
were covered by black coke.
Beyond temperature control of the
engine, another counter measure is to
prevent polymerisation of the degrad-
ed fuel that accumulates in the engine
oil. That requires steps to be taken
to prevent oxidation. Hirano said that
lubricant manufacturers will have to
do their part to make this happen.
Hirano acknowledged that degraded
fuel is unavoidable in real-life use of
gasoline-fueled engines. However,
reduction of insolubles formation is
possible. “In order to achieve better
anti-oxidancy of the engine oil, there
are two ways: better anti-oxidant for-
mulations and higher quality base oils.
These are very important to prevent
coking in the engine,” he said.
